Why does my rifle shift its aimpoint? – Part 2

by B.B. Pelletier

Part 1

Before I begin, I’m going to break my rule about commenting on forums. I read a thread about me on the Yellow Forum yesterday and was surprised to see some very complimentary remarks. I usually don’t get that. Several who commented also mentioned that they don’t agree with me all the time, and I’d like to say here and now – NEITHER DO I! I have changed my mind many times in the pursuit of this hobby and I bet I’m not done, yet. Just a few weeks ago I discovered a new wrinkle on the artillery hold that makes it work a lot better than the way I described it in the Beeman R1 book.

I’m not fishing for compliments, but I’d like to thank everyone who added to that thread.

Okay, to the task at hand. Our bore is clean, so let’s mount the scope and get to testing. With an AirForce Condor, however, there are some other things that should be checked. Barrel tightness is an important one. Four screws hold the barrel in the Condor, and if it’s a recent one the screws go through the bushings to contact the barrel. Older Condors have two long screws that contact the barrel and two short screws that contact the barrel bushings.

The other thing I checked was the clearance of the top hat. It’s set at the factory at 0.090″ clearance, and should be left there for best results. This one was okay. Then, I mounted the scope and tightened it down. I used an AirForce 4-16×50 scope I use on both my AirForce rifles. It’s in a prototype B-Square adjustable one-piece mount with ultra-high riser blocks. It provides too much elevation, but it works on every AirForce rifle I try it on, so scope mounting takes about one minutes. Time is money. Let’s shoot!

Shooting from the bench
I promised someone I would report about shooting techniques from a bench rest, so you probably think I have a high-tech bench to use in testing. Nothing could be further from the truth. My “bench” is a rickety folding table I drag from range to range. It’s a TV table on steroids. When I shoot PCPs, I use a long shooting bag filled with crushed walnut shells. The top is arranged in a “V” and the rifle lays between the upright legs. A slender Condor fits this bag perfectly.

 

The shooting bench. Real high-tech, eh? The first target is about 12 feet away. The one in the field is about 20 yards.
Sight-in at 10 feet
If you haven’t read my Sight-in article, I recommend you do so now. You don’t need boresighters, lasers or any other gimmicks to sight in an airgun. Just start shooting at 10 feet. Your goal is to get the pellet printing as far below the aimpoint as the center of the scope is above the center of the bore. Of course, you want to be aligned with the aimpoint vertically. The picture shows this much better than I can explain. Remember, this is shot at 10 feet. Because of the terrain on this range I had to shoot at 12 feet. Everything worked as it should.

 

At 10 feet (12 in this case), it’s hard to miss the paper. Shot No. 1 was low and to the right. The others were as the scope was dialed in. Four shots to zero and about five minutes.
Move to 20 yards
After you’re on at 10 feet, move to a target 20 yards away. Refine the sight adjustments until you’re on at that distance. This takes another 5 minutes (took three shots). On to 35 yards, because that was the distance at which Hegshen complained of point-of-aim shifts of 1-1.5 inches.

Move to 35 yards
At 35 yards, I started shooting JSB Exact 15.8-grain domed pellets with the power wheel on No. 4. On my Condor, that’s where I get great accuracy. But not on Hegshen’s rifle. The pellets were all over the place. His rifle has the latest valve (we checked it before I started this test), and we filled the air tank to 3,100 psi. After all the shooting I’d done to this point, the gun was probably down to 2,800-3,000 psi or so.

 

At 35 yards, these pellets are all over the place. The aimpoint is the center of this bull. The gun seemed to be shooting too slowly, so the power was turned up.
When pellets are all over the place and seem to be moving slowly (as these did), I turn up the power. In this case, I went to power setting No. 8. The point of impact climbed several inches, which was perfect, because I didn’t want to destroy the aimpoint.

This time, the pellets went to the same place, so I shot 20 rounds to see if there would be a point-of-impact shift. There was none. From this test, I know the rifle isn’t shifting its point of impact, so now we can move on to more likely culprits.

 

At 35 yards, these 20 shots give a good round group. The aimpoint was the center of the bottom bull. Yes, I see the pellet outside the group at 7 o’clock and also the one at 12 o’clock, but they’re meaningless. I did nothing to control the regularity of these pellets – no weighing, no inspecting of skirts prior to shooting – nothing. They were shot as they came from the tin. I wasn’t looking for a tight group (though I got one); I was looking for a point-of-impact shift that never occurred.
Before we move on, a word about this 20-shot group. It’s not a five-shot group. Had it been, it would have been about 0.30″ center-to-center. But, shoot 10 shots and that’ll increase to 0.70″. Shoot 20 shots and it increases again. The group that you see measures 1.124″ c-t-c. Could this rifle have done better had I shot a second 20-shot group? Of course. Could it have done worse? Absolutely. Don’t get hung up on the group size, because it doesn’t matter. Look at the shape. There is no POI shifting going on, and that’s all we care about today.

 

This shot was taken while the 35-yard, 20-shot group was being fired. There’s no high-tech shooting equipment being used and that scope is very high above the rifle. So, parallax is a potential problem. I dealt with it and kept it under control.
Now what?
Okay, the rifle is fine, so AirForce packaged it up and sent it back to Hegshen, along with the 35-yard target that I wrote some notes on. What if he still has the point-of-impact shift when he gets the rifle back?

I’m pretty sure he will, because I know what’s happening. When I was the technical director at AirForce, I took all the phone calls and emails about POI shifts and accuracy problems, and I have seen this happen many times before. Before I tell you what it is, let’s review this case. Hegshen told me he would get his rifle sighted-in, then come back to it several days later and the point of impact would have shifted. He also said that sometimes he would shoot five or six shots and then the point of impact would shift 1-1.5 inches to the left at 35 yards. He also told me his rifle shot to one side close up and to the other side far away. What’s wrong?

Parallax.

Look at the picture of me shooting the rifle. See how high my head is above the bore of the rifle? It has to be high because that’s where the scope is. If I do not put my face at the same point on the buttstock every time I shoot, my point of impact will shift, too. I’ve had to learn how to position my head in the same place shot after shot, or my POI would shift, too. But that’s not all.

Look at where the center of the 35-yard, 20-shot group is. Now look at where the first 35-yard group of shots with the lower power setting is. It’s several inches lower and slightly to the right. In other words, changing the power changes the point of impact. And, changing where you position your head changes the point of impact.

It’s difficult to see, but just in front of the scope on this rifle you can see a scope level. If you go back to Part 1 and look at the first picture, you can see it there, too. Hegshen has glued it to his rifle, which isn’t the best way to mount a level, but it works. I used that level on every shot to get the 20-shot group. Had I not, there would either have been point-of-impact changes or a larger group.

Here is what I’m telling Hegshen – and anyone else who experiences point-of-impact shift. First of all, the first shot from a cold rifle will probably not go to the same place as the shots that follow. That’s true for springers, for CO2 guns and for PCPs. It’s even true for firearms. Airgun barrels do not warm up as the guns are shot, but the valve of a PCP needs to be exercised occasionally to deliver consistent performance.

Second, you have to work on your hold, so your eye always ends up in the same place relative to the scope. This takes a lot of practice, but it returns more consistent groups.

Third, find a power setting and a single pellet and stick with both. Every time you adjust the power, you’ll have to sight-in the rifle all over again. Hegshen has been shooting Kodiaks, which are good pellets, but I recommend that he try JSB Exacts and Crosman Premiers. Both will outshoot Kodiaks in a Condor, as long as the power isn’t turned up all the way.

Fourth, if you want your groups to move straight up and down instead of from one side of the vertical reticle to the other, center your scope optically. Don’t take shortcuts. Do the labor and you’ll get the reward.

I’m not finished with this report, yet. There’ll be another part that covers all the other reasons for POI shift. But that will be another day.

32 thoughts on “Why does my rifle shift its aimpoint? – Part 2

  1. Hi B.B.,

    You said – “Fourth, if you want your groups to move straight up and down instead of from one side of the vertical reticle to the other, center your scope optically.”

    Ok, I know you have probably already covered how to ‘center your scope optically’ in another blog – would you please post the link for that?

    I’d like to go back over that blog & make sure I have done that. Thanks.


  2. Something unrelated – I recently installed a new spring in my .22 cal RWS 48, and after a couple dozen shots to set the new spring the power really seems to be up there. It’s doing over 25ft-lbs with 14.3gr Gamo Match pellets – almost 900fps with a spread of only 12fps over 10 shots. Crosman Wads are around 24ft-lbs with a spread of 15fps.

    This seems to be rather high for a ’48, but with the fairly tight velocity spread I don’t think it’s being artificially boosted by excessive lube burning. What do you think – is this within the realm of normal performance for this gun?

    Vince


  3. So, air rifles DO need a warm-up. I wondered and questioned that a couple weeks ago. I tend to frame my questions around hunting related problems encountered, but do you think before going on a hunt, you should fire off a few shots to warm-up and double check the aim point? Do you think the rifle would cool down and throw off the aim while you’re out hunting? I myself might try an expirament to see just that, but I want to know what you think of this warm-up issue. JP



  4. Vince,

    Your 48 is way above the norm. Of course it is burning fuel, because all breakbarrels that shoot faster than 600 f.p.s. do that. They all diesel. The question is, is it detonating? You don’t hear anything, so probably not.

    I’d say if you still have this high velocity after 1,000 rounds, you have a very special 48. Don’t get rid if it.

    B.B.


  5. JP,

    When I hunt with any gun I only consider the first shot. I have a Kreighof .30-06 that shoots to the POA on the first shot but walks away from the aim point with successive shots.

    So my preparation for hunting is to zero the gun (firearm and airgun) for the first shot and forget the follow-ons.

    B.B.


  6. BB

    just a thought, but i was interested in the other readers way of optically centering a scope. By putting it on a sheet of glass, which is itself on a mirror surely you are 100% dependent on the bell of the scope being absolutely flat, and perfectly formed? Im not suggesting that they arnt, but as i dont know that they are, thought someone else might do?

    paul


  7. B.B.

    My point-of-aim has shifted in bizarre ways but probably all due to my marksmanship.

    I’ve figured that a scope level can only help but are there cases–high scope mounts, long range–where it becomes a necessity?

    Credit where credit is due. I was delighted to find that the writer of this blog is Tom Gaylord but had thought that B.B. Pelletier was doing quite a good job.

    Matt61


  8. BB,

    I’ve read the Yellow Forum from time to time, and concider it to be a pretty good source of airgun info. But it’s not PA’s Blog. As far as I’m concerned, you never have to look for compliments. Because, when you’re the best at what you do, you’re the best.

    BobC NJ


  9. I like the centering technique. Must be great for those scopes it works for and those who adjust their scopes a lot and want to recenter. I only once bottomed out and counted half the revolutions of the entire movement to recenter.

    I’m not a high tech or an experienced shooter. Mainly I just hunt small game, shoot a few targets and old junk. Experimenting and reading a lot helps. I have some airguns that shift a little as you start shooting them fresh out of the case, but mainly lower cost bb guns. For hunting, a “cold” shot point of aim may be necessary and for targets a “warm” shot point of aim may be needed.

    Mounting a scope I generally rest my rifle on a level horizontally while aiming at a premeasured verticle door frame etc…to square off my scope when I mount it. Usually my eye piece is approx 2 inches from the scope or what the instructions recommend. I don’t adjust my scope once it’s set for the yardage that works for me. After that I just move my point of aim to adjust for range and wind.

    Consistancy in placing you cheek on the rifle is key and sometimes a piece of felt with double stick tape on the rifle helps. I also look a little above my scope and draw my head down just until the I get a clear picture to get a consistant view through the scope and make sure left to right looks center in the scope. I only have 4×32 scope with unadjustable parallax set at 30 yards or so.

    I have the most trouble with my springer. A consistant hold is needed for sure. I feel for the stock screws with cetain fingers and flatten my hand palm up on the stock with light hold over all. I let the springer jump where it wants to. Seems like its not going to shoot good groupings this way, but it does. Some shooter use the back of their hand with their fingers across the bottom of the stock. Some shooters use the back of their hand with their fingers parallel to the stock. I’ve even seen one shooter do this last hold while raising their index and pinky finger along side of the stock.


  10. Matt61,

    Certainly the higher your scope is mounted, the greater the effect from canting. Actually, canting starts to be a problem at about 30-35 yards. It depends on what level of accuracy you strive for. For an FT competitor, they want to put every pellet in the same hole, so canting at any range is bad. For a hunter, a miss of an inch may not matter – it depends on the game.

    B.B.


  11. BB and all,

    Talk about off topic!

    I travel alot, 10 days out of 14 and almost always it is not realistic to take any pellet guns along.

    How quiet are Airsoft guns? Quiet enougth to shook in a hotel room, say 15-20 feet or so? Would it help my pistol technique? How much for one that won’t be a toy in a week? Enough questions?

    Thanks for anybody’s input.

    Al Pettet


  12. Hi BB,

    Regarding parallax – If an AO scope is used with the parallax setting dialed in to the range of the target, does that reduce or even eliminate sensitivity to the position of the shooter’s head on the stock?

    Thanks,
    George in TX


  13. Al,

    I actually started with airsoft because I couldn’t visualize myself getting anything closer to a firearm. Now look at me waiting on a .30 caliber rifle. They were vital as a transitional stage, and to answer your question are extremely safe and quiet. They won’t pose a problem in a hotel room. I have a UHC Super 9 rifle and a 1911 spring pistol–I think the brand is KSC. They were even able to teach me shooting technique. The Super 9, which is a spring gun, clearly showed the superiority of the artillery hold over anything else. When I got into a routine, I was even able to get good accuracy out of it at 20 feet. After shooting pellet guns, though, both are too inaccurate to be satisfying. The 1911 remains useful to practice instinct shooting where you won’t be accurate anyway and quick draw techniques since you don’t have to worry about dropping the gun and shooting yourself.

    As an alternative, I would recommend the Daisy 747 pistol. This thing really is quiet. It will certainly blend in among whatever else goes on in the other hotel rooms, and it is extremely accurate. You can also get the small, portable Beeman pellet trap to go with it.

    Matt61


  14. Hey Al Pettit, I did the same thing as you for years, on the road all the time, put the trash can up in the corner and fill it with all the junk paper they give you in the room, a single stroke pnuematic or low power springer pistol will give you hours of enjoyment, never been even noticed at the front desk……


  15. Al,

    The first thing did with an airsoft pistol was set up a shooting range in my hotel room. I got the gun from Leapers at the 1999 SHOT Show in Atlanta. It was accurate enough to hit small hotel soaps at 25 feet, which is hardewr than it sounds.

    I can’t say that gun, for which I paid $20, was a high-quality one. I didn’t shoot it enough to find out. It still works today, but it doesn’t have 1,000 shots on it.

    You definitely want a spring gun to keep the noise down, but I’d look at the higher-end models.

    The Daisy 747 that was recommended is another quiet airgun, and far more accurate than an airsoft pistol. As long as you don’t fly, it would be a great gun, as well.

    B.B.



  16. B.B.,

    Great wright up. B-Square AA mounts are not cheap, but they seem more important than the scope in most occasions. I ordered 17101 for my R7 DG, I’m getting that horizontal shift with different ranges.

    When someone tells me that they know everything about a subject it turns me off. Like they have nothing else to learn. We don’t expect you to know everything. Just keep up what your doing.


  17. Cyberskin,

    i know how to program a VCR. lol

    i think theoben hit the nail hit the nail on the head with their mounts. The mounts are bolted into the receiver and on high tolerance square tracks that keep it in place. I saved me time over other guns without that feature but still settle on nothing less than perfect.

    i have been out for a while- good to be back

    -sumo


  18. B.B.,
    You mention that finding a particular power setting and sticking with it. That seems difficult w/ these airforce rifles the pressure drops after every shot and the rifle gets progressively faster. So, it seems these rifles have at least 3 varibles to contend w/: the power wheel, the progressive increasing power, parallex.
    Do other rifles experience the kind of power changes that the condor does?
    That’s why I don’t fill to 3K but to about 2800, but I still see the progression.

    Any tips,

    hegshen


  19. Hegshen,

    Interesting point. I haven’t tested this with a Condor, but I have with a .22-caliber Career 707. My old Career dropped in pressure very fast, but by adjusting the 17-position power wheel I could get 100 consistent shots at around 30 foot-pounds. It took a lot of time with a chronograph to figure out, but once I knew what I was doing, the adjustment was easy. I could keep all 100 shots within 30 f.p.s.

    B.B.


  20. I know this is hardly related to the article. But I think that The airforce condor is AWESOME and I definitely want to buy one first chance I get. However I am curious about how the bolt cycles, and I am also curious to know if it is ambidextrous(I am a lefty and left eye dominant). I have searched and searched the internet for information on this subject and it seems to be lacking.

    can you send me pictures of your condor/ and information as well? my email is Knightly@mail.com

    and also I am curious about the attachment for the condor to make it quieter you posted about it, but I can’t find anymore information on it, other then what you have said I even went to airhog.com and couldn’t find it. I live in a state where Silencers are illegal and it would save a lot of trouble and hassle if I could make a gun with such a loud report quieter.

    Thank you for your time and consideration, Knightly


  21. Knightly,

    The Condor bolt is pushed straight forward to cock the rifle, then, after loading, slide it back and rotate into one of the two notches at the rear of the receiver.

    All AirForce riflers are fully ambidextrous.

    We don’t send information directly. Call AirForce Airguns for additional information:

    877-247-4867.

    Call Airhog for more information on the frame exyender. They don’t have anything online about that product.

    B.B.


  22. Not sure how to ask you a question totally unrealated to this topic, so I’ll just ask here.

    I want to buy an air rifle for hunting but want to stay under $150. I’ve read alot of your posts and did research elsewhere and am down to a 392 or the Mendoza MR200. I don’t really care as far as multi pump or spring piston. I want accuracy, accuracy, accuracy and the ability to knock down small game efficiently out to 25 or 30 yards. Also, I’d like the gun to last. Will either suffice? Also, is there some other gun I should consider as well?

    Thanks



  23. Is the 513M $60 better, or would I be ahead if I spent that $60 on a scope and mounts or a peep sight (which I’m more likely to do)? Also, would the addition of a peep change the thought process for me?

    Thanks

    Gunny


  24. Gunny,

    That’s a tough question, but since you ask, I would go with the scope and the Mendoza. Better sights beat more power any day. The peep is also a good choice, and being military, you should be used to one. Remember, you can always upgrade.

    B.B.


  25. I really appreciate it. The mendoza trigger will also be similar to the Savage .308 w/ Accutrigger I use to deer hunt…also, I like the idea of the lighter trigger…my .308 is set right around 2 lbs.

    Any other thoughts about the MR200 that are not in your reviews?

    Thanks Again

    Gunny



  26. Gunny,

    No need to apologize. I’m lisdexic, too.

    The RM-200 is over-lubricated as it comes to you. Short of a complete disassembly, which I don’t know how to do, myself, there’s nothing to do but shoot it a lot. There will a be a prolonged period of smelling burned oil and perhaps a crack or two of detonation in the beginning. Just keep shooting it and things should smooth out around 1,000 shots.

    I think the main thing is to find good pellets for it. It likes the largest pellets you can find. Right now, that might be a Gamo Hunter or Gamo Magnum. Try Daisy pointed pellets, too, as they are sometimes very large.

    Please tell me how you like the rifle, after you’ve played with it awhile.

    B.B.


  27. After going back and looking at the specs, now I’m unsure again. The extra power may be nice as I’d like to be able to sit in my bow blind and pop crows and squirrels at aroun 40 yards, but as I mentioned, the RM200 will probably handle more like my deer rifle and one of the other reasons for buying the air rifle for me is to shoot in order to get better with my other rifles.

    I have a couple weeks to make a decision, so I’ll probably change my mind 50 times in that thime period. :)

    I’ll let you know how I like whichever one I buy

    Thanks

    Gunny


  28. Top tip for target shooting… Place your gun on a stable surface, put your eye in the sweet spot move your head around a little. If you see the reticle shift up/down or left/right relative to the target then you need to tweak the AO/parallax ring. Keep doing this until there’s no movement.

    Once completed and assuming your shooting from the same spot you should find your accuracy has increased significantly.


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